Recently, the unidirectional spin Hall magnetoresistance (USMR) has been observed experimentally as thesecond harmonic component of the longitudinal resistance R_(2ω) in several non-magnetic metal(NM)/ferromagnetic metal (FM) bilayers. The USMR is applicable to magnetic random-access memories(MRAMs) . The mechanisms have been proposed as the modulation of the interface resistance due to thespin accumulation by spin Hall effect (SHE) and/orelectron spin-flip scattering by excited magnons. In arecent work, magnons are mainly responsible for theUSMR in the high-temperature regime . R_(2ω)includes not only the USMR but also thermoelectriceffects and spin-orbit torques (SOT). In the high-fieldregime, however, SOT can be excluded andthermoelectric effects still remain. Here, we try tomeasure the temperature dependence of the USMRconsidering thermoelectric effects to discuss themechanism of USMR in NM/FM bilayers.Figure 1 shows the scanning electron micrographsof our device consisting of NiFe(5 nm)/Pt(10 nm)Hall bar. We can measure simultaneously the secondharmonic resistances in both geometries, (a) and (b).In geometry (a), we can obtain the combined signalsof the USMR and thermoelectric effects while onlythermoelectric effect appears in (b). At a giventemperature ranging from 10 to 290 K, we measuredR_(2ω), R_(2ω)~H while sweeping a magnetic field from -200to 200 mT. Figures 2 and 3 show the results at 10 Kand 290 K, respectively. As shown here, thetemperature variation in the USMR is prominent incomparison to the thermoelectric effects.
展开▼
